Interpretive Summary: Thymol and carvacrol are major constituents in the essential oil of thyme. Although both are well known antioxidants and antimicrobial agents, their low solubility in water has greatly limited their use on food products. The present study investigated the effects of particle size and solution pH on the solubility of these natural compounds. Results showed that encapsulating thymol and carvcrol with corn protein via a nano technology significantly improved their solubility without diminishing their antioxidant and antimicrobial capacities. Adoption of this new technology will enable the food and produce industry to expand postharvest application of thymol and carvacrol to improve the quality and safety of fruits and vegetables.

Technical Abstract:
Thymol and carvacrol, two isomeric terpenoids found in the essential oil of thyme, were encapsulated in nanoparticles of the corn protein zein using a liquid-liquid dispersion method. The morphology, antioxidant properties, and antimicrobial activity were determined for nanaparticles formed under acidic, neutral, and basic pH conditions. Regardless of pH, the nanoparticles were well dispersed in water and stable for more than 3 weeks. After lyophilizing, samples from the acidic solution tended to form a film, whereas samples from the neutral and basic conditions formed nanoparticles. Antioxidant properties were analyzed by 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) and ferric ion-generated hydroxyl radical spectrophotometric assays. DPPH• was scavenged in the range of 24.8 - 66.8 % depending on the formulation and more than 65% of hydroxyl radicals were quenched by all three samples. A 0.8-1.8 log CFU/ml microbial reduction was achieved in the presence of nanoparticles encapsulating thymol plus carvacrol.